Motorcycles and other small vehicles typically use a hand throttle to regulate the speed and acceleration of the vehicle, as opposed to using a gas pedal. The hand throttle is generally used in a rotary manner, so that the rider twists the hand throttle to increase the speed from minimum (idle) to maximum. The hand throttle is linked to a carburetor or fuel injected throttle body, and this linkage allows the twisting of the hand throttle to control the operation of the carburetor or throttle body by controlling the amount of fuel and air that flows through the carburetor or throttle body.
FIG. 2 illustrates elements of a carburetor 2, as mounted on an engine 1. The carburetor 2 is a device that mixes air and fuel for an internal combustion engine. The majority of older motorcycles are carbureted and new motorcycles are fuel injected. The carburetor and fuel injection system works on Bernoulli's principle, which is that moving air has lower pressure than still air, and that the faster the movement of the air, the lower the pressure.
The air flow in the carburetor 2 is controlled by rotational movement of a bell crank 3, which is connected to butterfly valves (not shown) in the interior of the carburetor 2 through movement of the butterfly shaft 4. The rotation of the bell crank 3 is implemented by movement of a push cable 5 and a pull cable 6 which are attached to the bell crank 3. Barrel wire end fittings 8 at the end of the cables 5, 6, are lodged in capture notches 9 in the bell crank 3 to secure them. Thus, there is a type of pulley system created by which the throttle on the handle acts to rotate the bell crank 3 and thus open and close the internal butterfly valves through the butterfly shaft 4.
Acceleration of the vehicle ranges from a minimum, where the engine idles, to maximum acceleration, and the opening of the butterfly valves in the carburetor or throttle body over this range can vary from a gradual increase over a relatively large angular twist range of the hand throttle to a very sharp increase from minimum to maximum over a relatively small twist range of the hand throttle.
If the carburetor or throttle body control is sensitive to angular rotation, a small rotation of the hand throttle will result in a large carburetor or throttle body adjustment. Conversely, if the carburetor or throttle body control is less sensitive, the hand throttle twist range between minimum and maximum acceleration will be larger, allowing finer control. This degree of control or sensitivity will be referred to as the “throttle rate”. A throttle which goes from minimum to maximum in a small angular range will be referred to as having a “fast rate”, and one which has a large throttle angle range will be referred to as having a “slow rate”.
Different rates are useful for different situations and environments. For example, a rider in the desert who is on very flat terrain with no obstacles may be primarily interested in applying maximum acceleration as quickly as possible, and therefore a more sensitive throttle with a fast rate may be preferred. Conversely, a rider in the woods who is operating in hilly terrain, or in rain or mud-slickened conditions, may want to have more precise control, and thus a less sensitive throttle with a slow rate is preferred.
Typically, a vehicle is configured to have a fixed throttle rate, which is not variable. Modifying the throttle rate is not an operation which is easily done.
Thus, there is a need for a throttle which can be easily modified to produce a variety of throttle rates to provide varying sensitivity and thus variable throttle control.